Plate-type heat exchangers comprise at least one pair of spaced-apart plates sealed together at their margins. Each plate pair defines a fluid flow passage having an inlet opening and an outlet opening. In a typical heat exchanger, the edges of the fluid flow passage have a height which is less than the height at the center of the fluid flow passage. The reduction in height adjacent the edges may be due to the manner in which the plates are joined together and/or the edges of the plates may be somewhat rounded as in U.S. Pat. No. 5,636,685 to Gawve et al.
The fluid flow passage may contain a conductive insert to enhance heat transfer and to increase turbulence in the fluid flowing through the flow passage. These conductive inserts, which are also known as turbulizers, usually comprise strips of metal in which a plurality of convolutions are formed by stamping and/or rolling. The convolutions are usually of a uniform height and are preferably in contact with both plates of the plate pair to maximize heat transfer. Numerous types of turbulizers are known in the prior art. One type of turbulizer which may be used in vehicular oil coolers is the louvered fin described in U.S. Pat. No. 4,945,981 (Joshi) issued on Aug. 7, 1990. Another type of turbulizer for use in vehicular heat exchangers is the offset strip fin, examples of which are described in U.S. Pat. No. Re. 35,890 (So) and U.S. Pat. No. 6,273,183 (So et al.). The patents to So and So et al. are incorporated herein by reference in their entireties.
As illustrated in FIGS. 1 to 3 of Gawve et al., a turbulizer of constant height cannot fill the entire area of a fluid flow passage which is reduced in height adjacent its edges, while maintaining effective contact with the plates. This causes the formation of a fluid bypass B (FIG. 3 of Gawve et al.) adjacent the edges of the fluid flow passage, which lowers the efficiency of heat transfer. This problem is partially solved in Gawve et al. by indenting the fin walls to reduce their height adjacent their ends, thereby reducing the bypass area B′ as shown in FIG. 7.
While the Gawve et al. patent addresses the problem of bypass flow, it is specific to corrugated fins extending transverse to the direction of fluid flow and having fin walls which extend across the entire width of the turbulizer. There remains a need to address the problem of bypass flow in heat exchangers using other types of turbulizers, such as the offset strip fins mentioned above.